1. Field of the Invention
This invention relates to information storage and processing devices and, in particular, is concerned with optical information carriers, methods for erasing information in such optical carriers, and optical memories realizing such method.
2 . Description of the Prior Art
Known in the art is an optical information carrier (GB,B, No. 1580398) comprising two disks disposed coaxially so that a space available between them is limited by two coaxial separating elements to form an enclosure. A recording medium is provided on one of the opposing surfaces inside the closed space.
Also known in the art is an optical information carrier (GB,B, No. 1580398) comprising a hollow cylinder, a recording medium applied on the external surface thereof, and a second cylinder enclosing the first cylinder. Disposed between the two cylinders are two resilient sealing elements which confine a cylindrical closed space adjoining the recording medium.
The known optical information carriers are deficient in that the connection between the disks and separating rings or between two cylinders is temporary and an adhesive material is used. This is required to develop the information after it had been recorded on the recording medium and, to this end, access to the recording medium is necessary.
The known optical information carrier cannot provide adequate protection of the recording medium from dirt since its internal space is not air-tight. Cyclic day-night changes in the temperature of the environment result in that dust and moisture is sucked into the internal space of the carrier together with air and the recording medium surface is gradually coated with dirt. One more disadvantage of the known optical information carrier is that it cannot provide multiple rewrite capability because of the dirty surface of the recoridng medium of the carrier.
Known in the art are also memory devices (FR,B, No. 2482756) comprising an optical information carrier made as a disk comprising a base and a recording layer whereon information is recorded by way of light beams.
Also known in the art is a method of erasing information, which consists in that recorded portions of the medium are exposed to a light beam so that they are reversibly brought into a state with the initial optical properties, this exposure changing the degree of crystallization of the recording medium therein.
This method is deficient in that information recorded on such a carrier is easily damaged by, for example, sun radiation or heat.
The erasure method takes too much time because the carrier has to be heated slowly and the desired temperatures has to be kept very precisely.
The method for erasing information described above is not efficient. Repeated recordings are not reliable because recording-erasing cycles adversely affect the structure of the recording layer and its thickness becomes non-uniform. This sharply reduces the number of rewrite cycles.
Also known in the art in an optical memory (U.S. Pat. No. 4,403,318) comprising an optical information carrier, an information recording and reading unit, an erasing unit, and a selection switch to choose recording, reading, or erasing modes of operation.
Known in the art is a method for erasing information recorded on an optical carrier (U.S.A. No. 4,403,318), which consists of a carrier is exposed to an external source for erasing information, e.g. by generating two or more light beams, focusing them on the optical carrier, and scanning these beams along the recording layer on the optical carrier so that portions of this recording layer are heated to different degrees. This is achieved by changing the light beam density by changing the radiation intensity or the size of the spot.
These prior art methods are deficient in that they cannot provide multiple use of optical carriers for the same reasons as described above.